This invention relates to vinyl ethers which are extremely reactive monomers, known to undergo polymerization either by a cationic or a free radical mechanism and are useful in applications which require a high speed curing of a resin formulation. Vinyl ethers react much faster than the epoxy resins and therefore may be used for such applications as printing inks, coatings, elastomers, foams and other types of products dependent upon the ability of the resin to cure at a rate which is consistent with other processing steps.
This invention relates to fluorinated vinyl ethers and more particularly relates to such fluorinated compounds containing one or more oxyvinyl groups. "Oxyvinyl group" as used herein means a vinyl group connected to the remainder of the compound through an ether oxygen atom.
Some fluorinated chemical compounds are known in the art which contain oxyvinyl groups such as are described in U.S. Pat. No. 2,732,370 under the generic formula C.sub.n F.sub.2n+1 CH.sub.2 --O--CH.dbd.CH.sub.2. The compounds F--(CF.sub.2).sub.3 --CH.sub.2 ----O--CH.dbd.CH.sub.2 and F--(CF.sub.2).sub.3 ----O--CH.dbd.CH.sub.2 are commercially available from the company "Monomer-Polymer & Dajac". The foregoing known compounds have fluorinated structures near the oxyvinyl group and are thus believed either not to be radiation curable or not to have radiation curable reactivities to the extent desired. Further, due to the heavily fluorinated structure, adherence to substrates and compatibility with solvents and cosolutes may not be as good as desired.
Continuing development of a new coatings has led to the need for improving performance in certain applications. Such improvements can include control of flexibility, hardness, moisture resistance, and low surface energy.
One known methodology used to modify the properties of coating materials is to employ nonionic fluorochemical surfactants. These surfactants have been shown to achieve lower surface tension. It is also known to those skilled in the art, that the use of additives which are not inherently bonded in the matrix of the resin can result in decreased performance as a function of time due to migration or removal as a natural consequence of abrasion or handling. There is therefore a need for a chemically bonded material which can impart novel characteristics to resins, without loss of activity, and which is chemically miscible with the components of a matrix under investigation.
The use of photocuring technology has grown rapidly within the last decade. Photocuring involves the radiation induced polymerization or crosslinking of monomers into a three dimensional network. Photocuring has a number of advantages including: a 100% conversion to a solid composition, short cycle times and limited space and capital requirements.
Photocuring technology has been applied in planar waveguide applications. See, B. M. Monroe and W. K. Smothers, in Polymers for Lightwave and Integrated Optics, Technology and Applications, L. A. Hornak, ed., p. 145, Dekker, 1992. In its simplest application, a photocurable composition is applied to a substrate and irradiated with light in a predetermined pattern to produce (the light transmissive) or waveguide portion on the substrate. Photocuring permits one to record fine patterns (&lt;1 .mu.m) directly with light. The refractive index difference between the substrate and the light transmissive portion of the substrate can be controlled by either regulating the photocurable composition or the developing conditions.
Because of the dramatic growth in the telecommunications industry there is a need to develop photocurable compositions for optical waveguide and interconnect applications. In order to be useful in these applications, the photocurable composition must be highly transparent at the working wavelength and possess low intrinsic absorption and scattering loss. Unfortunately, in the near-infrared region, among which the 1300 and the 1550 nm wavelengths are preferred for optical communications, conventional photocurable materials possess neither the required transparency or low intrinsic absorption loss.
The absorption loss in the near-infrared stems from the high harmonics of bond vibrations of the C--H bonds which comprise the basic molecules in conventional acrylate photopolymers. One way to shift the absorption bands to higher wavelengths, is to replace most, if not all, of the hydrogen atoms in the conventional materials with heavier elements such as deuterium, fluorine, and chlorine; e.g. as described by T. Kaino, in Polymers for Lightwave and Integrated Optics, Technology and Applications, L. A. Homak, ed., p. 1, Dekker, 1992. The replacement of hydrogen atoms with fluorine atoms is the easiest of these methods. It is known in the art that optical loss at 1300 and 1550 nm can be significantly reduced by increasing the fluorine to hydrogen ratio in the polymer. It has been reported that some perfluorinated polyimide polymers have very low absorption over the wavelengths used in optical communications. See, S. Ando, T. Matsuda, and 5. Sasaki, Chemtech, 1994-12, p. 20. Unfortunately, these materials are not photocurable.
U.S. Pat. No. 5,274,174 discloses a new class of photocurable compositions comprised of certain fluorinated monomers, such as diacrylates with perfluoro or perfluoropolyether chains, which possess low intrinsic absorption loss. It is, therefore, possible to make low loss optical interconnects from a photocurable system including these materials.
Fluorine substitution in the polymer structure, however, also induces some other less desirable changes in the polymer's physical properties. One such change is the decrease in refractive index. For a highly fluorinated acrylate photopolymer, the refractive index decreases to the 1.32 region when the H/F mole ratio reaches 0.25. For optical interconnect applications, to avoid loss of light, it is important that the refractive index of the core of a planar waveguide approximate and preferably match that of the optical fiber (generally 1.45). Another problem with fluorine substitution in the polymer is the decrease of the surface energy of the resulting photopolymer film which results in its reduced adhesion to other materials such as found in substrates.
It is also important to be able to precisely control and fine tune the refractive index of the photopolymer at the working wavelength in optical waveguide and interconnect applications. A desired index of refraction can be produced by mixing photocurable monomers with different refractive indices. Most photopolymers made from conventional photocurable monomers have refractive indices in the region of 1.45-1.55. Depending on the application, it is often desirable to lower a photopolymer's refractive index. One way to do this is to mix low refractive index fluorinated monomers with conventional hydrocarbon-based monomers. Unfortunately, this is difficult to accomplish because of the incompatibility or insolubility of the different monomer systems. Thus, there is a need for photocurable compositions which: (I) possess low optical loss in the near-infrared region, (II) possess a refractive index approaching traditional optical fibers; and (III) are compatible with both conventional hydrocarbon-based and highly fluorinated monomers.